« previous next »
Pages: [1]   Go Down

Author Topic: Cb750 cylinder head and block stuck together  (Read 423 times)

0 Members and 1 Guest are viewing this topic.

Offline Jcop.550

  • Enthusiast
  • **
  • Posts: 127
Cb750 cylinder head and block stuck together
« on: October 15, 2023, 10:42:22 AM »
Started tearing into my engine today. The cylinder head and block/jugs came off in one. Can’t get them to split. Soaked and applied some heat but they are really stuck. I prefer not to bang or pry at it to avoid damage. Any tips or tricks to getting these split?



Sent from my iPhone using Tapatalk
Logged

Offline PeWe

  • Really Old Timer ...
  • *******
  • Posts: 15,580
  • Bike almost back to the 70's 2015
Re: Cb750 cylinder head and block stuck together
« Reply #1 on: October 15, 2023, 10:50:13 AM »
All 4 M6 bolts under rubber coins + the 2 M6 on each side of cam xhain tunnel removed?
Logged
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Jcop.550

  • Enthusiast
  • **
  • Posts: 127
Cb750 cylinder head and block stuck together
« Reply #2 on: October 15, 2023, 10:57:39 AM »
Quote from: PeWe on October 15, 2023, 10:50:13 AM
All 4 M6 bolts under rubber coins + the 2 M6 on each side of cam xhain tunnel removed?
Yep, all removed. Triple checked as it was driving me nuts!


Sent from my iPhone using Tapatalk
Logged

Offline PeWe

  • Really Old Timer ...
  • *******
  • Posts: 15,580
  • Bike almost back to the 70's 2015
Re: Cb750 cylinder head and block stuck together
« Reply #3 on: October 15, 2023, 11:16:21 AM »
Can be a sticky headgasket.
I had got one late 1979. I remember it was sticky on both side before assembly. Think it was Honda gasket.
It sat a few seasons, but think I needed sharp tools.

Or only 2 very tight dowel pins. Use heat on the front outer holes were they sit.

Or a PO have used Permatex all over the gasket to fight leaks?
« Last Edit: October 15, 2023, 11:18:06 AM by PeWe »
Logged
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Jcop.550

  • Enthusiast
  • **
  • Posts: 127
Re: Cb750 cylinder head and block stuck together
« Reply #4 on: October 15, 2023, 12:36:25 PM »
Quote from: PeWe on October 15, 2023, 11:16:21 AM
Can be a sticky headgasket.
I had got one late 1979. I remember it was sticky on both side before assembly. Think it was Honda gasket.
It sat a few seasons, but think I needed sharp tools.

Or only 2 very tight dowel pins. Use heat on the front outer holes were they sit.

Or a PO have used Permatex all over the gasket to fight leaks?
Yeah definitely is. Bike sat for 30+ years which doesn’t help either. Thanks for the advice


Sent from my iPhone using Tapatalk
Logged

Offline BenelliSEI

  • Really Old Timer ...
  • *******
  • Posts: 9,958
  • 1969 cb750
Re: Cb750 cylinder head and block stuck together
« Reply #5 on: October 15, 2023, 02:08:31 PM »
Before you start beating on it, check again. Last time I was getting really annoyed I found “one more”…….
Logged

Offline madmtnmotors

  • When did I get to be a
  • Really Old Timer ...
  • *******
  • Posts: 6,108
  • Sunny Central Florida
Re: Cb750 cylinder head and block stuck together
« Reply #6 on: October 15, 2023, 03:24:51 PM »
I had an engine that some "super-goob" had used some sort of industrial adhesive on both sides of the head gasket. I finally found two spots between the head and cylinders that will tolerate a great deal of force. Look carefully at the back of the head/cylinder assembly near the 1/2 intake and the 3/4 intake. There should be extra material at each of these locations that will accept more prying force without fin damage. When I finally got mine apart the head gasket actually delaminated with half the head gasket stuck to the head and the other half of the gasket stuck to the cylinders.

Damn P.O.'s...
Logged
TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                          
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline Jcop.550

  • Enthusiast
  • **
  • Posts: 127
Re: Cb750 cylinder head and block stuck together
« Reply #7 on: October 15, 2023, 03:38:42 PM »
Quote from: madmtnmotors on October 15, 2023, 03:24:51 PM
I had an engine that some "super-goob" had used some sort of industrial adhesive on both sides of the head gasket. I finally found two spots between the head and cylinders that will tolerate a great deal of force. Look carefully at the back of the head/cylinder assembly near the 1/2 intake and the 3/4 intake. There should be extra material at each of these locations that will accept more prying force without fin damage. When I finally got mine apart the head gasket actually delaminated with half the head gasket stuck to the head and the other half of the gasket stuck to the cylinders.

Damn P.O.'s...
Thank you for this! I’ll check it out and give it a try. It seems like the only way these will split is by prying which I was afraid of damaging the fins.


Sent from my iPhone using Tapatalk
Logged

Offline Phoenix

  • Hot Shot
  • ***
  • Posts: 273
  • 4 wheels move the body. 2 wheels move the soul
Re: Cb750 cylinder head and block stuck together
« Reply #8 on: October 15, 2023, 05:28:50 PM »
May be a really stupid idea but....what if you put the jugs in a bucket of ice water overnight and then heat the next day.  Then pry.  Good luck.
Logged
Ed Spengeman
Indy
1971 CB750K1 (Stock)
1973 CB350 Twin  (Gone)

Offline Jcop.550

  • Enthusiast
  • **
  • Posts: 127
Re: Cb750 cylinder head and block stuck together
« Reply #9 on: October 16, 2023, 12:41:33 PM »
Got it! Heat lightly, pry, and repeat and a lot of patience.


Sent from my iPhone using Tapatalk
Logged
Pages: [1]   Go Up
« previous next »